1. Technical Field
The present invention relates to a method and device for controlling a haptic interface. More particularly, the present invention relates to a method and device for controlling a haptic interface, which may maintain stability and enhance transparency by limiting force under conditions that energy generated in the haptic interface, a sample-and-hold unit, a controller and a virtual environment satisfy passivity conditions.
2. Description of the Related Art
Greater operational interactivity has become possible with the development of computer graphics technology, and interest in virtual environment technology has increased as graphics hardware becomes cheaper, and thus there have been realized a number of virtual environment systems available for various fields such as entertainment, military training, surgery training, education, biomedical simulation, engineering design, simulation, etc. In the virtual environment technology, haptic technology is one of research fields indispensable to maximize reality through a realistic virtual environment in which a user can further immerse themselves. Through various haptic interfaces, a user can feel tickling sensation and tactile sensation and interact with the virtual environment.
In order to provide correct force and torque information to a user through haptic simulation, stability is one very important factor in the field of haptic research. As research on such a stable haptic interactive system, Colgate and Schenkel have proposed a virtual coupling algorithm having virtual connection between a virtual environment and a haptic interface for stable haptic display (J. E. Colgate and G. G. Schenkel, “Passivity of a class of sampled-data systems: Application to haptic interfaces,” J. Robot. Syst., vol. 14, no. 1, pp. 37-47. (1997)).
Meanwhile, Hannaford and Ryu have proposed a time domain passivity theorem (B. Hannaford, and Jee-hwan Ryu, “Time Domain Passivity Control of Haptic Interfaces,” IEEE Trans. On Robotics and Automation, vol. 18, pp. 1-10. (2002)). Through a passivity observer/passivity controller (PO/PC) under a short sampling cycle, the time domain passivity theorem observes energy input and output in real time and consumes total energy to stabilize the system at every sampling time.
Also, Ryu et al. have proposed a new PO capable of estimating energy generated in a zero-order holder when the sampling period is long (Jee-hwan Ryu, Y. S. Kim and B. Hannaford, “Sampled and Continuous Time Passivity Control,” Proc. IEEE Int. Conf. On Robot and Automation, Taipei, Taiwan. (2003)). Further, they have proposed a reference energy following method where a real energy input follows reference energy varied in time so as to prevent a haptic device from trembling at high frequencies due to sudden change in force (Jee-hwan Ryu, B. Hannaford, C. Preusche, and G. Hirzinger, “Time Domain Passivity Control with Reference Energy Behavior,” Proc. IEEE/RSJ Int. Conf. on Intelligent Robotics and Systems, Las Vegas, USA. (2003)). Preusche et al. have extended the time domain passivity theorem to multiple degrees of freedom, which has an advantage in that there is no need to know a correct kinetic model of the haptic interface (C. Preusche, G. Hirzinger, J. H. Ryu and B. Hannaford, “Time Domain Passivity Control for 6 Degrees of Freedom Haptic Displays,” Proc. IEEE/RSJ Int. Conf. on Intelligent Robotics and Systems, Las Vegas, USA. (2003)).
In the meantime, Kim and Ryu have proposed an energy bounding algorithm as a conventional method of stabilizing a haptic interface (J. P. Kim and Jeha Ryu, “Stable Haptic Interaction Control Using Energy Bounding Algorithm,” IEEE/RSJ Int. Conf. Intelligent Robots and Systems (IROS2004), Gyeongju, Korea. (2004)). This algorithm can efficiently consume the energy generated in the zero-order holder even when the sampling period is long. The energy bounding algorithm limits the energy generated in the zero-order holder within a range of energy consumable by a physical damping value of the haptic interface, thereby satisfying passivity conditions.
However, such a haptic interface device used in haptic interaction does not generate energy, but a sample-and-hold unit and a control system generate energy, causing instability of the whole system. Moreover, conventional technologies have numerous design restrictions in stabilizing the haptic system, and deteriorate reality in an adjustment process for stabilization.